1. Field of the Invention
The present patent application relates to the field of radar gauges in radar level gauging systems, and particularly to radar gauges allowing for a prevention of interference in the level gauging system as well as a method for such prevention.
2. Description of the Related Art
Radar level gauges are commonly used today for measuring the level of the surface of a product kept in a container, such as a tank. Two different types of radars are principally used in such level gauging, pulse radar gauges and Frequency Modulated Continous Wave (FMCW) radar gauges. The pulse radar uses the pulse-shaped amplitude modulation of the wave to be radiated and determines the direct time interval between transmission and reception of the pulses. The FMCW radar determines the transit time in an indirect way by emitting a frequency-modulated signal and differentiating between the emitted and the received instantaneous frequency.
In certain applications, such as the process industry, there are a need for installing more than one radar gauge, e.g. for redundancy purpose and/or using one radar gauge for level control and another for measuring. The presence of two or more radar gauges in the same container will lead to a certain interference between these gauges. This problem is negligible for an FMCW radar gauge type, but is serious for a pulse radar gauge type. This is due to the fact that an FMCW radar only listens within an interval of about 100 kHz, while a pulse radar is open to the whole frequency band. A pulse radar transmits short pulses in the size of nanoseconds (ns) modulated around one frequency, e.g. 6.3 or 26 GHz, while an FMCW radar is scanning the frequency within a defined frequency band, e.g. 9.5–10.5 GHz.
In the case when more than one pulse radar level gauge is installed in a container, the pulses from one radar level gauge will interfere with the measuring of the other radar level gauge(s) and vice versa, unless the radar level gauges transmitting pulses, transmit these pulses in a synchronized manner or by other means separated.
Therefore, it would be desirable to provide a method and an arrangement for preventing interference between radar level gauges installed in a container for measuring the filling level of a product kept in the container. A method and arrangement which are possible to apply to already existing radar level gauges.